1. Field of the Invention
This invention relates to marine propeller drive systems for boats and, more particularly, to a marine propeller drive system having an articulated propeller shaft incorporating a constant velocity joint.
2. Description of the Prior Art
Over the years, three systems have become preferred for marine propeller drive systems. These are known as "outboard", "inboard-outdrive" and "inboard" propeller drive systems. Each of these have distinct operating features and characteristics that determine which of these is the system of choice for a particular application.
The outboard propeller drive system has a self-contained motor and drive train for the propeller which is mounted aft of the boat, onto a specially adapted mounting structure built into the transom. It has the advantage of easy servicing, as the motor can be easily removed from the boat. More importantly, it has the advantage that the unit as a whole rotates when a turn is initiated. This means that the propeller thrust axis is caused to rotate into the turn, which greatly improves handling at low speeds and makes single propeller maneuvering when in reverse relatively easy. The outboard propeller drive system, however, has the disadvantage of being expensive because of mechanical complexity. Further, it is inefficient because a substantial structure is located below the water surface, resulting in viscous drag. Additionally, the point of contact of the propeller drive system with the boat is at a location on the transom high above the hull, resulting in thrust from the propeller drive system not being aligned with the hull. Finally, these outboard propeller drive systems tend to add considerable weight aft of the transom, frequently resulting in difficulty in achieving proper planing of the boat at low to moderate speeds of operation.
The inboard-outdrive propeller drive system has the motor contained in the boat itself, but the propeller drive mechanism is contained in an external outdrive unit which is aft of the transom. Generally, the external outdrive unit is secured to the transom and articulates relative thereto, functioning much like the propeller drive of an outboard propeller drive system. The inboard-outdrive propeller drive system has the advantage that commercially available engines, after marine modification, may be used, thus, substantially reducing costs. Further, because the external outdrive unit rotates when a turn is initiated, the propeller thrust axis rotates, as in the outboard propeller drive system, thus, greatly enhancing low speed and reverse maneuvering capability.
There are numerous examples of inboard-outdrive propeller drive systems. U.S. Pat. No. 3,136,287 to North is exemplary of an inboard outdrive, and also generally exemplary of the complex mechanical linkage frequently associated with inboard-outdrive propeller drive systems. North attaches his external outdrive unit to a tiltable intermediate member which is in turn attached to the transom. A universal joint allows tilting and steering of the external outdrive unit. Many other inboard-outdrive propeller drive systems have been developed, including U.S. Pat. No. 3,368,516 to MacDonald et al which utilizes a constant velocity joint; U.S. Pat. No. 3,368,517 to MacDonald et al which utilizes a Cardan universal joint; U.S. Pat. No. 3,382,838 to Bergstedt which utilizes an inclined drive shaft and bevel gear; and U.S. Pat. No. 3,826,219 to Nossiter which utilizes a drive transmission that permits articulation without use of universal joints. U.S. Pat. No. 3,487,804 to Kiekhaefer is of interest to show an improved inboard-outdrive propeller drive system incorporating an air stream at the propeller to reduce viscous drag. The inboard-outdrive retains many of the advantages of the outboard, while retaining essentially all of its disadvantages, as enumerated above.
The inboard propeller drive system has the motor and transmission entirely contained within the boat. Most commonly, a propeller shaft exits from the hull forward of the transom and angles downwardly to a point near the transom. In these systems, the propeller shaft is not articulated, and the propeller is retained in a fixed relationship with respect to the hull. Because of the fixed position of the propeller, it is very difficult, if not impossible, to steer the boat when operating at low speeds or in reverse. To solve this problem, it is well known in the art to provide two spaced apart propeller shafts. By operating the propeller shafts at different angular velocities, it is possible for the skipper to achieve a torque couple that will steer the boat. While a second propeller shaft can aid low speed and reverse maneuverability, it is expensive and is not generally as maneuverable as the inboard and inboard-outdrive propeller drive systems. Inboard propeller drive systems have the advantage of utilizing conventional motors and transmissions which are adapted for marine use, thus, reducing the expense of these components. Further, the torque axis generated by the propeller is generally in line with and directed onto the hull, thereby greatly aiding the performance characteristics of the boat.
One form of the present invention relates to inboard propeller drive systems that incorporate propeller shafts which exit the boat through the transom. A particular case in point is an inboard propeller drive system for surface effect propellers. Surface effect propellers are utilized in high performance boat applications, where it has been found that the propeller efficiency is highest when it operates partially out of the water. Accordingly, in these surface effect propeller drive systems, the propeller shaft is located on the transom near the waterline. An example of a surface effect propeller drive system is U.S. Pat. No. 3,933,116 to Adams et al. Adams et al disclose a marine propeller drive system having an articulatable propeller shaft incorporating a double-Cardan universal joint, a propeller cover, and a thrust bearing box for the propeller shaft. The propeller is able to articulate in the vertical as well as the horizontal directions. Propeller thrust is transferred to the transom at the attachment location of the thrust bearing box. A second example of a surface effect propeller drive system is U.S. Pat. No. 4,565,532 to Connor. Connor discloses an articulatable propeller shaft incorporating a double-Cardan universal joint, a gimbal ring mounting for the propeller shaft and a vertically stacked gear box. The gear box requires extensive structure aft of the transom. Propeller thrust is transferred to the transom where the gear box attaches to the transom. Both the Adams et al and Connor marine propeller drive systems involve complicated structures, requiring disposition of the propeller far aft of the transom. Further, the mounting and drive structures of the Adams et al and Connor marine propeller drive systems require mounting to the transom, thereby precluding operation in situations involving conventional inboard marine propeller systems where the shaft is mounted under the hull. Additionally, the Adams et al and Connor marine propeller drive systems utilize double-Cardan universal joints which, although sometimes referred to incorrectly as "constant velocity universal joints" are not actually constant velocity universal joints as shaft vibration is present caused by speed variations in the joint. Finally, the Adams et al and Connor marine propeller drive systems deliver propeller thrust generally onto the transom, an undesirable feature, since for best performance and maneuverability, propeller thrust should be delivered to the boat at the hull, in line with the propeller shaft.
Hence, there remains in the art the need to provide an inboard propeller drive system which has the capability of providing the maneuverability of outboard and inboard-outdrive propeller drive systems, while substantially retaining the external structural simplicity and hull directed propeller thrust delivery of conventional inboard propeller drive systems. There further remains in the prior art the need to provide the aforesaid maneuverability and hull directed propeller thrust delivery utilizing a true constant velocity universal joint, as exemplified by the Rzeppa type.